1. Field of the Invention
The invention relates in general to a complementary metal oxide semiconductor (CMOS) image sensor and method of manufacturing the same, and more particularly to a CMOS image sensor, including a non-single-crystal-silicone-base substrate and transparent gate electrodes, and method of manufacturing the same.
2. Description of the Related Art
In the era of technology with rapid advances, image sensors have been widely applied in the fields of television, toys, security systems, scanners, mobile phones, digital video cameras, digital cameras, and many other portable electronic devices. Currently, there are at least two types of image sensors, which are a charge coupled device and a CMOS image sensor. Owing that CMOS image sensors can be mass-produced in semiconductor manufacturing process, their production costs can be relatively reduced. The features of low cost and low power consumption make CMOS image sensors more and more popular in the market.
FIG. 1 shows a lateral view of a conventional CMOS image sensor. In FIG. 1, the CMOS image sensor 100 includes at least a silicone substrate 102, a source 104, a drain 106, a gate dielectric layer 108, polysilicon gate electrodes 110, and 112, an interlayer dielectric layer 114, a passivation layer 116, and metal electrodes 118, 120, and 122.
The silicone substrate 102 includes a charge-generating region 150 as shown by the dotted line in FIG. 1, and the source 104 and the drain 106 are formed in the silicone substrate 102. A pre-channel region 140 is formed between the source 104 and the drain 106, and the source 104 is located between the charge-generating region 150 and the pre-channel region 140. If the silicone substrate 102 is slightly p-type doped [P−], the source 104 and the drain 106 are heavily n-type doped [N+]. The gate dielectric layer 108, formed on the silicone substrate 102, covers the source 104 and the drain 106.
The polysilicon gate electrodes 110 and 112, formed on the gate dielectric layer 108, are respectively located above the charge-generating region 150 and the pre-channel region 140. The interlayer dielectric layer 114, formed on the gate dielectric layer 108, covers the polysilicon gate electrodes 110, 112, and has an opening 132 between the polysilicon gate electrodes 110 and 112. The metal electrode 118 fills the opening 132 and covers a part of the interlayer dielectric layer 114. The passivation layer 116, formed on the interlayer dielectric layer 114, covers the metal electrode 118. In addition, the passivation 116 has openings 124 and 126, respectively located above the source 104 and the drain 106. The metal electrodes 120 and 122, formed on the passivation layer 116, are respectively deposited in the openings 134 and 136 to be connected with parts of the interlayer dielectric layer 114 at two sides of the polysilicon gate electrode 112.
Moreover, the polysilicon gate electrode 110 and the charge-generating region 150 form a photo detector, and the polysilicon gate electrode 112, the source 114, and the drain 116 form a reset transistor. The metal electrode 120 is an electrode for discharging charges. When light is sensed by the CMOS image sensor 100, a bias is applied on the polysilicon gate electrode 112 so that the reset transistor can equalize the charges in the source 104 and the drain 106. Another bias is, subsequently, applied on the polysilicon gate electrode 110 to make the charge-generating region 150 as a depletion layer. The incident light passes the passivation layer 116, the polysilicon gate electrode 110, the gate dielectric layer 108, and arrives the charge-generating region 150, the depletion layer, to excite charges. The charge-generating region 150 having excited charges, the metal electrode 118, and the source 104 will thus form a charge transfer transistor. A bias is, afterwards, applied on the metal electrode 118 to transfer the charges excited in the charge-generating region 150 to the source 104 and make the charges on the source 104 more than those on the drain 106. A constant bias voltage (VDD) is then applied on the metal electrode 122 to discharge the charges in the source 104 until they are equal to those in the drain 106. Therefore, the intensity of the incident light can be determined by measuring the amount of charges that are discharged from the metal electrode 118. The more intense the incident light is, the more charges are discharged from the metal electrode 118. These discharged charges are accumulated to form a corresponding image.
Since the silicone substrate 102 is very expensive, the production cost will be considerably high. In addition, for a part of the incident light is absorbed by the polysilicon gate electrode 110, it will make an error on the sensing result and the sensing image to be distorted, thereby reducing the image quality.